1. Field of the Invention
The present invention relates to a mobile communication apparatus and an intermittent receiving control method, and more particularly to a mobile communications apparatus and an intermittent receiving control method capable of reducing power consumption by performing variable control of an intermittent ratio of receiving in standby mode.
2. Description of Related Art
Generally, mobile communications apparatuses such as mobile phones carry power supplies in the form of batteries. Accordingly, it is necessary for them to reduce their power consumption in the standby mode to prolong the battery life. To achieve this, their receiving stages operate not continuously but intermittently at fixed time intervals in the standby mode so as to receive radio signals from mobile communications networks.
The ratio of the receiving operation time to the standby time in the intermittent reception is referred to as an intermittent ratio. Reducing the intermittent ratio can reduce the power consumption. However, if the intermittent ratio is too small, it becomes difficult for the mobile communications apparatuses to receive enough system information from the mobile communications network. For example, when a mobile communications apparatus moves across neighboring cells, it cannot achieve proper handover but for the sufficient system information.
Thus, various mobile communications apparatuses have been conventionally proposed which reduce power consumption by carrying out variable control of the intermittent ratio in accordance with radio environments. Such mobile communications apparatuses are proposed, for example, in Japanese patent application laid-open Nos. 4-322523/1992 and 9-261153/1997.
The former discloses a mobile communications apparatus that reduces its power consumption by varying the intermittent ratio in accordance with the size of a visited cell informed from a base station. Generally, as the size of the visited cell increases, the probability also increases for the mobile communications apparatus to be present in the same cell. However, when the mobile communications apparatus is on a periphery of the cell, it sometimes cannot select an appropriate intermittent ratio. In addition, in a small visited cell, the mobile communications apparatus cannot reduce the intermittent ratio in accordance with its moving speed, and hence cannot reduce power consumption.
The latter discloses a mobile communications apparatus that increases the intermittent ratio when a good receiving condition continues for a fixed time interval, and reduces the intermittent ratio when the receiving condition is bad. However, the receiving condition does not always correspond to the distance to the cell center. Furthermore, the good receiving condition in the past does not necessarily promise a good receiving condition in the future.
In particular, when the mobile communications apparatus moves fast, or when the cell itself moves as in a satellite communications system, the positional relationships between the mobile communications apparatus and the cell varies greatly, resulting in frequent occurrence of the handover. In addition, when the cell itself moves, because the relationships between the visited cell and its neighboring cells varies from time to time, the system information also changes every moment.
Thus, if it is possible to predict the future positional relationships between the mobile communications apparatus and the visited cell, and to variably control the intermittent ratio in response to the prediction, the proper system information can be obtained with reduced power consumption.
According to a first aspect of the present invention, there is provided a mobile communications apparatus comprising: a receiving processor for intermittently receiving a radio signal, and for extracting from the radio signal location information about a reference point in a visited cell; a distance calculator for obtaining a distance from the mobile communications apparatus to the reference point; a distance comparator for comparing distances obtained by the distance calculator; and an intermittent ratio controller for controlling an intermittent ratio of the receiving processor in response to an output of the distance comparator. With such an arrangement, the mobile communications apparatus can detect the changes in the distance to the reference point in the visited cell, and control the intermittent ratio of the receiving processor in response to the detected result.
Here, the intermittent ratio controller may reduce the intermittent ratio of the receiving processor when the distance comparator outputs a signal indicative of reduction in the distance over a predetermined time period. This makes it possible to prevent the fluctuations in the intermittent ratio.
According to a second aspect of the present invention, there is provided an intermittent receiving control method comprising: a receiving step of intermittently receiving a radio signal; an extracting step of extracting, from the radio signal received, location information about a reference point in a visited cell; a distance obtaining step of obtaining a distance from a mobile communications apparatus to the reference point; a distance comparing step of comparing distances obtained by the distance obtaining step; and an intermittent ratio controlling step of controlling an intermittent ratio of the receiving step in response to a comparing result. This makes it possible to detect the changes in the distance from the mobile communications apparatus to the reference point in the visited cell, and to control the intermittent ratio of the receiving operation by the mobile communications apparatus in response to the detected result.